Filter network



Oct. 17, 1939. O H. R. BUTLER ,1

FILTER NETWORK Original Filed Aug. 28, 1937 4 sheets-Sheet 1 CONTROL PANEL CONTROL CONTROL PANEL PANEL MULTl-PHASEA-O. POWER SOURCE INTEGRATION NETWORK COMPOSITE FILTER- NETWORK 3/ IN VEN TOR. 3m 3/5 3/ HEIIIH R. Hut] E1" Byg s I I RANS A E ATTORNEY Oct.-l7, l939.', m -rm 2.1 .04

FILTER RETWORK Original Filed Aug; 28, 1957 4 sheets sheet 2 Flcs- E f T I INTEGRATION NETWORK COMPOSITE FILTER I N Q'IWORK 3/a 3/6 J/ L j *a/d' J/e I POWER. 4/ AMP.

DRIVER 40 AMP,

SIDE BAND 39 FILTER MODULATI'IQ 38 AMP.

MODULATOR 37 someone v INVENTOR. HARMDNIC 1 36 GENERATOR HEnr- H.1Elufler I BY MAs'rR v ATTORNEY I 35osmLL 'r-0R.

Oct. 17, 1939. H. R. emu-m 2,176,046

' FILTER NETWORK Original Aug. 28, 4 s e s f 4 INVENTDR;

HEflr- R. HIIHEI BYQ \L 'l,

A TTORNEY Patented Oct. 17, 1939 UNITED STATES were PATENT OFFICE FILTER NETWORK Henry R. Butler, Verona, N. J.,' assignor to Wired Radio, Inc., New York, N. Y., a corporation of Delaware 3 Claims.

5 filed August 28, 1937.

The principal object of the invention consists in providing a distribution system for hotels, apartment houses and the like, as well as other restricted and localized areas involving special distribution problems.

A further object of the invention consists in producing a multiple program-channel distribution system for simultaneously transmitting over a common transmission medium a plurality of programs at discrete frequencies and within a condensed frequency range.

A further object of the invention consists in providing a multiple channel program distribution system having composite networks common to all of the channels for integrating the transmission characteristics of all of the channels with respect to a common transmission medium for effecting constant transmission conditions.

A still further object of the invention comprises providing a wired radio service system embracing a multiplicity of service group net- Works each including a plurality of service sections, together with an arrangement for integrating the characteristics of the groups and sections to provide uniform transmission.

These and other objects will be apparent from the following, reference being had to the accompanying drawings which form a part of this specification and in which like reference numerals designate corresponding parts throughout, and in which:

Fig. 1 is a schematic representation of one embodiment of a wired radio service system in accordance with the invention;

Fig. 2 is a schematic representation of the transmission equipment employed in the system of Fig. 1;

Fig. 3 is a diagrammatic representation of a composite network employed in the system depicted in Fig. 1; and

Fig. 4 is a graphical representation of certain transmission characteristics of parts of the sys tem of the invention.

The system of the invention contemplates the provision of plural channel selective program service for a multiplicity of subscribers or consumers centrally located in a hotel, an apartment house, or a community, and involving diverse conditions of electrical transmission. In such a transmission area, involving variant electrical conditions including the use of many forms of power consuming apparatus, changing loads, and many other adverse conditions, it has been found extremely difficult to effectively and efficiently transmit carrier frequency energy to a multiplicity of receivers in the area so that all of the subscribers or consumers at dififerent points of reception will have the benefit of a program of uniform quality and strength. This is true for a single program of a moderate range of audio frequencies, and a problem of much greater proportions arises when it is desired to simultaneously transmit many programs each of high fidelity characteristics embracing a Wide range of audio frequencies.

According to the invention, a portion of the carrier frequency spectrum is utilized in which carrier frequencies may be transmitted most efiiciently, and the plurality of program channels are electrically condensed so that they can all be accommodated within this favorable range. Further than this, applicant utilizes composite networks for integrating the effects of the electrical characteristics of the plural channels against the common transmission medium, so as to bring about an effective transmission of plural program channels of wide range audio frequency characteristics to a great number of reception points, and with uniform signal strength and quality at these many reception points.

The transmission network The invention will be described in connection With a hotel structure, although it will be recognized that the inventive concept is applicable to effect program transmission in other situations involving similar difficulties and problems. Referring to the drawings, the schematically represented hotel structure is divided into a plurality of vertical distribution sections I, 2, and 3. These sections extend vertically through the building and include a partial area of each floor, the fioor areas over one another being aligned. Each floor is provided with wire lines 4-H which are electrically isolated in accordance with the vertical sections I, 2, and 3. The floors are further divided into groups 12 and [3, the group I2 including floors 4-l and the group I3 including floors 8--l I.

At a suitable location, such as in the service basement of the building, control panels l4, l5 and I6 are provided to serve commercial power and wired radio signals to the vertical sections I, 2 and 3. These control panels each comprise suitable equipment such as switches, fuses, etc., for exercising supervisory control over the composite energy distributed to the vertical sections.

Composite bus system 20 supplies both commercial power and signalling energy to the control panels I4, I5 and H5. The bus system 20 comprises a neutral line 2|, power voltage phase lines 22, 23, and 24. The lines 22-24 are connected to capacitors 25, 26 and 21 and thence to a terminal of a composite integration network 28, the other terminal of this distribution network being connected to the neutral line 2|. The bus system is also connected with a multiphase alternating current power source 30 which supplies three-phase alternating current to the bus system, the phase lines 22, 23, and 24 each carrying 110 volt alternating current with respect to the neutral line 2|.

From control panel It, riser cables Ma and Mb serve the groups l3 and I2 of section I. Similarly, riser cables l5a and I5?) originate at control panel l5 and energize groups l2 and I3 of section 2, and riser cables Ito and I 61) serve groups l2 and E3 of vertical section 3. These riser cables each comprise three lines in which, as shown in Fig. 1, the central line is neutral and the side lines are at 110 volts potential for commercial alternating current with respect to the neutral line. It will be noted that each of the floors in a group served by riser cables are connected in sequence to different ones of the 110 volt lines, the neutral line of the cable being commonly connected with all of the floor circuits in the group.

The transmitter equipment The integration network 28 is connected through the composite filter network 3| having branches 31a, 3lb, 3lc, 3ld, and M6, which are respectively connected with transmitters A-E. The transmitters A-E produce modulated high frequency energy corresponding to five different programs comprising the five different program channels transmitted in accordance with the invention.

Referring to Fig. 2, a master oscillator 35 produces Waves of a base frequency which, in the present embodiment of the invention, is 13 kilocycles, A harmonic generator 36 is driven by the master oscillator 35, and produces electrical waves which are amplified harmonics of the base frequency of the master oscillator 35. These harmonies are separately fed to modulator amplifiers 38 of the respective transmitters A--E. The frequencies of the oscillation waves delivered to these modulator amplifiers are, in the present instance, 26, 39, 52, 65, and 78 kilocycles, respectively. The modulator amplifiers 38 respectively amplify these various frequencies and, at the same time, modulate the same with the modulation frequencies derived from the various modulation sources 3'! of the transmitters AE. The outputs of the modulator amplifiers 38 are delivered through side band filters 39 which limit the output frequencies in a definite and predetermined manner as will be pointed out hereinafter in more detail.

The modulators 38 are of the variable carrier type, the carrier frequency varying in amplitude in accordance with the impressed modulation frequencies. In another arrangement, the modulators maybe of the fixed carrier type. Again, and to obtain certain other desired objectives, the modulators 38 may be of the suppressed carrier type wherein the carrier itself is suppressed, and only the frequencies in a side band adjacent the carrier frequencies are transmitted as, for instance, disclosed in copending application of R. C. Curtis, Serial No. 155,213, filed July 23, 1937, which issued March 21, 1939, as Patent No. 2,151,- 464. The details of a transmitter system for transmitting with fixed, variable, or suppressed carrier are disclosed in an application of Edmund A. Laport, Serial No. 50,491, filed November 19, 1935, now Patent No. 2,089,561, issued August 10, 1937.

The side band filters 39 respectively feed into intermediate driver amplifiers 40 which control the output power amplifiers M of the transmitters AE. The power output, comprising modulated high frequency energy within definite frequency limitations, is fed by the power amplifiers 4| into respective branches 31a to 3 le of the composite filter network 3|. The composite filter network 3! and the integration network 28 cooperate and interact between the transmitters AE and the transmission medium to effect a level controlled and segregated distribution of the frequencies of the different channels simultaneously transmitted by the transmitters AE.

Transmission frequency characteristics Fig. 4 graphically represents the transmission frequency conditions of the system of the invention. The harmonic generator 36 (Fig. 2) prosupplied to the various transmitters from the various different program sources 31 AE are each for an extensive range of audio frequencies. In the present instance, a range of 8,000 cycles per second is used, although wider ranges can be utilized in accordance with the invention.

Such audio frequencies acting upon the carrier frequencies will produce upper and lower side bands. For example, the audio frequencies acting upon the carrier frequency C1 of transmitter A will produce upper and lower side bands represented by curve 3A1 and SAZ extending respectively upon opposite sides of the carrier frequency C1. Similarly, the other carrier frequencies C2 to C5 may be modulated to produce upper and lower side bands represented by curves designated by the letter S with corresponding subscripts.

Referring to Fig. 4, it will be seen that the carrier frequencies are all spaced within a relatively narrow range C to C1,, found by experiment to be the most effective part of the carrier frequency range for transmission over networks carrying other forms of electrical energy. The spacing of the carrier frequenciesCi to C5 on the frequency spectrum is by increments of the base frequency, which is 13 kilocycles. Thus the separation between any two of the carrier frequencies is 13 kilocycles. Since, by comparison, any one of the side bands is quite wide in extent, it will be seen that there is considerable overlapping between the upper side band. of ne channel and the lower side band of the next channel above on the frequency spectrum. Thus the side band SAZ overlaps the side band $131 for approximately 20 kilocycles.

According to applicant's invention, all the channels are condensed so that only the lower side bands 8A1, S131, etc. are utilized. Therefore, frequencies substantially from only the lower side bands Sm to SE]. are impressed upon the electrical circuits common to all the channels. The process of frequency condensing is effected by the filters 39 of the transmitters and the other common networks of the system. 7

The frequency transmissions of the filters in combination with the network 3 I, are represented by the curves TA-TE. The transmission characteristics of these filters definitely determine the extent and position of the pass band of frequencies so that width 50 is substantially less than the frequency range of one of the channels extending between any two of the carrier frequencies, there being, in. addition, a guard frequency range 5| between each of the curves TA-TE. The right hand slopes of the curves TATE as shown in Fig. 4 are centered on the carrier frequencies C1-C5, the points all being along the level indicated by the line 52. The line 52 represents substantially one-half of the total transmission level represented by the height of the curves TA-TE. It will be seen therefore that within the range 53, both the upper and lower side bands are transmitted, but with compensating decrements so that the effective level in this range is substantially the same as the level for the remainder of the single side band of frequencies transmitted. It will be seen that the two ranges 54 and 55 comprising the halves of the range 53 are of equal extent on opposite sides of the carrier frequency. Such a condition is true for each of the frequency channels, it being noted that the frequency channels AE do not coincide precisely with the ranges defined by the frequencies C1-C5.

Composite filter and integration networks Referring to Figs. 1 and 2, it will be seenthat the transmitters AE and the distribution network are inter-connected by the integration network 28 and the composite filter network 3|, connected in tandem, and represented in detail in Fig. 3. Referring to Fig. 3, the branches 3| al tie comprise a part of the filter network. These filter networks have a plurality of filter sections 80, El and 62. It will be seen that the first two sections, 50 and BI, of the filter are included in the branches 3 let-3 Ie, whereas the last section of each of the filters is included in the network 62, which is common to all of the various filters associated with the channels AE. That is, each channel operates through a filter comprising a plurality of sections, and one section of each filter is represented by a network common to all of the filters.

The section 60 includes coupled inductances B3 and 64 and capacitors 65 and 66 connected as shown. The section BI comprises the coupled inductances 61 and 68, and the capacitors 69'and 70 connected as shown. All of the sections 60 and GI of the filter branches 3Ia and 3Ie have similar components, indicated with corresponding subscripts, the value of the parameters of these components being designed in accordance with the frequencies peculiar to the respective program channel associated with the various filters.

The section 62 comprises parallel lines 10 and TI. Coupled inductances 12 and I3, and capacitors I4 and I5 are connected between the lines 70f and ll, as shown. Coupled inductances 11, I8 and capacitors I9 and 80, are also connected between the lines 101 and 'II, as shown. Unconpled inductances 8|, 82 are respectively connected in series with capacitors 83, 84, as shown.

The output circuit of composite filter 3| includes a circuit comprising the inductance 90 and capacitor 9| connected as shown. This output circuit is shunted by a primary winding 92 of a transformer 93 having secondary windings 9t, 95, 95 91, and 98. These secondary windings are coupled by inductances I00, IOI, I02. I03, I04 and capacitors I05, I06, I01, I08, I09 to line H connected to output terminal III. The output terminal H2 is connected at a point between the secondary windings 9B and 91.

It will be noted that the inductances 63 have a midpoint connection to the power amplifiers M. The latter are of push-pull type and the midpoint connection is to the balance point of the circuit interconnecting the push-pull tubes of the amplifiers. In this arrangement, the anode supply of the push-pull amplifiers 4| traverses the inductances 63, these inductances therefore forming part of the anode circuits of the push-pull amplifiers.

The integration network 28 includes reactive components having parameters calculated to give a general transmission characteristic for the general frequency range Co-C1. as represented by the curve H in Fig. 4. This curve has definite level points of equal magnitude along the line II6 intersecting the carrier frequencies C1- C5, and is arrived at by solving five simultaneous equations involving the output impedance from terminals III and H2 looking into the transmission medium, the equations being solved for the five carrier frequencies for desired conductance and zero susceptance of the primary input of the transformer.

The curve II5 represents the effective transmission levels of the pass range of the integration network 28. It will be seen that all of the curves TA to TE will be accommodated by the curve I I 5, with appropriate level control for all of the frequencies with respect to the level control mean line H6.

The networks 28 and 3| in tandem cooperate by virtue of the segregated circuit components and the common circuit components, and interact between the transmission medium and the transmitters AE to produce a uniform distribution of carrier frequency signals as before set forth, so that each of the multiplicity of receivers B may receive any one of the simultaneously transmitted program channels with high fidelity and uniform reception among the channels with respect to a particular receiver, and with uniform reception with respect to allof the receivers located at the various points.

The values for the parameters of the components of networks 28 and 3| are as follows:

TABLE or CIRCUIT PARAMETERS Inductances in millihenries Part Nos. Value Part Nos.

Capacities in The relations of the transformer ratios for the input transformer of the integration network are 45 as follows:

TABLE or TRANSFORMER TURN RATIOS Parts Nos. Ratios Although a preferred form of wired radio service system has been disclosed in connection with particular circuit arrangements and components and specific parameter values for such components, it will be recognized that various changes, modifications, and equivalent arrangements can be made without departing from the intended scope of the invention. Therefore, no limitation is intended except as pointed out by the appended claims.

I claim:

1. A wave filter network comprising, a plurality of wave filters adjusted to pass frequencies within different frequency bands and each comprising a plurality of filter circuit sections, the circuit components of the last section of all of said filters being connected in a common network offering the proper individual section impedance for said filters, and the frequency bands thereof, while, at the same time, accommodating all of said frequency bands in a general frequency range, said common network including a plurality of series resonant circuits connected across paralleling lines interconnecting the section output terminals of all of said filters.

2. A wave filter in accordance with claim 1 including an output circuit for said terminating network including a transformer and a network connected therewith having taps at different turn ratios, all of said taps being connected with resonant circuits all of which are individual to the different frequency bands of said filters.

3. A wave integration system comprising, a plurality of pass band filters adjusted to pass frequencies within different frequency bands, and including a network common to all of said filters for combining the bands of frequencies thereof in a general frequency range, a transformer connected with said common network for producing a plurality of different voltages in said different frequency bands, and a network connected with the secondary of said transformer and having a plurality of reactive components adjusted to be responsive to only particular frequencies at particular voltages, all of said components being connected together in parallel in a common network having the values thereof adjusted in accordance with the interacting values of all the other components.

HENRY R. BUTLER. 

